IMPORTANCE OF WINDS AND RAINS 



193 







pressures all about them, we may know that there the air 

 tends to circle about this center, converging toward it, 

 and moving upward as it reaches the center. We can 

 also understand that this whole great rotating mass of air 

 tends to move also in the direction of the prevailing winds 

 which push upon it. 



The arrows of Fig. 69 indicate the movement of air 

 in such a cyclone as viewed from above, while those in 

 Fig. 70 indicate 

 these movements as 

 viewed from the 

 side, assuming that 

 the prevailing winds 

 are from left to 

 right. 



Another kind of 

 cyclone is the anti- 

 cyclone. Its center 

 is a center of high 

 pressure. In it the 

 air moves downward 

 and outward instead 

 of inward and up- 

 ward. For the rea- 

 son you have already learned, you can understand that 

 cyclones in the southern hemisphere rotate in the reverse 

 direction from those in the northern hemisphere; their 

 rotation, whether the movement be inward or outward, 

 is influenced by the earth's rotation as well as by the differ- 

 ence in atmospheric pressure. 



} It is a frequently observed fact that rain or snow com- 

 monly accompanies areas of low pressure, while clear 



FIG. 6g. Diagram showing the direction of winds 

 around areas of high (H) and low (L) pressure, 



when viewed from above . N ?nd s indicate 

 S Uthem hemispheres -- After 



